HANOI: Vietnam's most powerful leader has called for greater unity among South-east Asian states as the country appears increasingly isolated in challenging China's territorial claims in the South China Sea.

Making the first visit by a Vietnamese communist party chief to Indonesia, Mr Nguyen Phu Trong said in a speech televised at home yesterday that Asean needed to be unified in resolving territorial disputes.

"Do not let Asean become a playing card for the competition among major countries," Mr Trong said.

Vietnam has emerged as the most vocal opponent of China's claims in the South China Sea, through which more than $3 trillion in cargo pass every year.

To China's annoyance, Vietnam held out at an Asean meeting this month for language in a communique that noted concern about island-building and criticised militarisation in the South China Sea.

Chinese pressure forced Vietnam to stop drilling for oil last month in a Vietnamese oil block that China claims. Beijing has also been angered by Vietnam's growing defence links with the United States, Japan and India.

Some Asean nations are wary about the possible repercussions of defying Beijing by taking a stronger stand on the issue.

China claims most of the South China Sea, while Taiwan, Malaysia, Vietnam, Philippines and Brunei claim parts of it. The area commands strategic sea lanes and has rich fishing grounds, oil and gas deposits. - REUTERS